Nearly 200 million “shell eggs” are consumed in the United States (US) each day. “Shell eggs” are non-powdered conventional eggs that are naturally produced by hens. Shell eggs are among the most nutritious foods on earth and can be part of a healthy diet. However, some unbroken, clean, fresh shell eggs may contain bacteria that can cause foodborne illness. While the number of eggs affected is quite small, 30% of the US population is highly susceptible to bacteria that may be found in eggs. Pregnant women, infants and young children, the elderly, and the immunocompromised are particularly at risk. Shell eggs topped the list of “Riskiest Federal Drug Administration—Regulated Foods” and had the most documented outbreaks from 1990 to 2006. The US Department of Agriculture estimates that pasteurization of all shell eggs in the US would reduce the annual number of illnesses by more than 110,000.
Currently only two companies in the US pasteurize shell eggs. Both companies use a hot water immersion process whereby the eggs are submerged in hot (approximately 56.7° C.) water for about 60 minutes. While long exposure to high temperatures is required to pasteurize the egg yolk, the high temperatures damage and degrade the quality of the albumen. Albumen damage can occur when the albumen is subjected to a temperature of 57° C., or held at 49° C. for 60 min. The albumen damage is manifested by varying amounts of coagulation and/or denaturation. By contrast, egg yolk can withstand temperatures of 64° C., or more, without being damaged.
Attempts have also been made to pasteurize eggs using microwave-based processes and at least one prior art patent discloses the use of radio frequency (RF) energy to pasteurize shell eggs. However these prior art processes proved to be inefficient and damaging to the targeted eggs.
Penetration depth of electromagnetic energy increases as the frequency decreases. Thus RF energy, in the range of 10 to 100 MHz can have a penetration depth ten times greater than that of microwave energy (2.45 GHz). Consequently, the deeper penetration of RF energy should heat the yolk better than microwave energy.
The current inventors' method and apparatus uses RF energy to directly and preferentially heat the egg yolk as the targeted egg is rotated, rather than to first heat the albumen and then the yolk (as is conventionally done by conduction heating a non-rotating egg). By using RF energy to heat the egg yolk directly, the process described herein is more efficient and avoids damage to the albumen. The inventors' method and apparatus quickly heats the yolk to inactivate pathogenic bacteria using RF energy. After the yolk reaches pasteurization temperature, the albumen is rapidly pasteurized using conventional methods. The net effect of the inventor's disclosed method and apparatus is to rapidly pasteurize shell eggs with minimal damage to quality and significant savings in time and other resources.